Method of producing black, metalcontaining surface layers



United States Patent 2,5 4 Claims. (Cl. 117-223) The invention relates to a method of producing black, metal-containing surface layers.

It is known that various metals can be coated with a thin molybdenum or tungsten layer by sintering and subsequent reduction of the corresponding oxides.

The present invention provides a method of producing black, metal-containing surface layers consisting of molybdenum and/or tungsten in the form of metal or an oxygen-containing compound, bound to the oxide or the hydroxide of at least one of the following elements: Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba. The invention also relates to the case in which subsequent to partial reduction an oxide of M0 or W remains, which is bound to an oxide of at least one of said elements. The black surface layer can be formed on a great number of different metals, for example nickel, molybdenum, copper, iron and various kinds of steel.

This black coating is obtained in a simple manner by the reduction of the molybdate or tungstate of the said elements or by starting from a mixture thereof. It is also possible to obtain said layer by applying to the metal substrate a compound of M0 or W and a compound of one of the said elements so that by a reaction at a high temperature in a reducing atmosphere molybdenum or tungsten in the form of the metal and of a given oxide or a hydroxide or, as the case may be, an oxygen-containing compound of Mo and/or W with at least one of the said elements is formed.

The method according to the invention consists in that a polymolybdate of lithium particularly the trimolybdate 3MoO .Li O is used, which material is particularly suitable for objects which should not be heated in excess of a temperature of 600 C. to 700 C. The substrate coated with a solution of this molybdate and then heated at about 600 C. in a reducing atmosphere, very soon assumes a black surface layer.

The immersion of a metal tape in a solution of this trimolybdate in equal parts of water and alcohol with a density of 1.12 gms./cm. provides a uniformblack layer adhering excellently. To this solution may be added a suitable quantity of a binder in order to vary the viscosity and wetting properties of the suspension employed. A colloid solution formed for example by 8 gms. of nitrocellulose in 140 mls. of ethylene-glycol and 60 mls. of butanol constitutes, with the solution of lithium-polymolybdate, a pseudo-solution which is particularly suitable for application by spraying, by means of a painting roller or by other similar methods.

The trimolybdate 3MoO .Li O, subjected to a reduction at comparatively low temperature (about 600 0), provides, by heating in hydrogen, a pitch black layer. A hydrogen-nitrogen atmosphere provides a violet-black layer, probably due to the presence of a small quantity of molybdenum oxide. An incomplete reduction may leave as an alternative, molybdenum bronze of the formula MoO .Li (x51). At any rate products of an incomplete reduction of this polymolybdate are not essential for this invention, if the surface layer contains oxidized or non-oxidized molybdenum, bound to an oxide-containing compound of lithium.

In some cases it may be desirable to remove any trace assignor Inc., New York,

of the binder of the lithium-molybdate solution. A rapid heating in air at 350 C. of the coated object will, in general, suffice to this end. A nickel tape, heated in air at 350 C. for 5 minutes, assumes a bluish black layer of lithium-molybdate, which excellently adheres to the substrate and which may provide inter alia a decorative effeet. The present invention thus relates to a coating which is obtained by complete or partial reduction of the applied molybdate.

The following examples, which relate to parts of electron tubes, provide a few possibilities of use of the method according to the invention for obtaining black layers. It is known that in most receiver tubes the anode must be capable of dissipating the heat produced by electron bombardment for the greater part by radiation and it is furthermore important that in operation the anode should not liberate products likely to poison the electron emission of the cathode or to cause an adverse eifect on the characteristic curve for example by a reduction of the vacuum. Experience has shown that nickel-plated steel provided with a black layer according to the present invention fulfils these conditions. Tubes particularly sensitive in this respect were provided with anodes consisting of a nickel-plated steel tape With a black surface layer. It was found that these tubes were more stable (after a duration of 1000 hours of operation) than tubes, the anodes of which were made of the conventional material, that is Feralrna (steel sheath covered on both sides with aluminum), Niferalma (steel sheath covered on one side with nickel and the other side with aluminum) and nickel having a black carbon layer.

The nickel-steel tape was provided by spraying with a suspension of 3MoO .Li O in ethanol diluted with Water in a ratio of 1:1 and a density of 1.12 gms./cm. and with the same quantity of collodium. The layer was dried by passing the tape along an infrared lamp, which heated the tape at 350 C. in air, after which the tape was sintered in hydrogen at 650 C. for five minutes.

In the same manner a cathode nickel tape Was treated, but only on one side, in order to improve the heat-exchange with the heating wire. The layer remained black after one hour of heating in vacuo at 1000 C. (vacuum of 2.10- mm. Hg).

With satisfactory success grids of molybdenum wire and tungsten wire on grid frames of various materials were blackened in order to reduce the electron emission to a negligible extent and to improve the heat radiation.

As a matter of course, the example described above do not restrict in any respect the use of the invention, which may also be applied to obtain decorative effects on jewels, gold ornaments, for protection against corrosion and so on.

What is claimed is:

1. A black surface layer on a metal substrate consisting of an oxidic compound of a metal selected from the group consisting of molybdenum and tungsten and an element selected from the group consisting; of Li, Na, K. Rb, and Cs.

2. A method of forming a black surface layer on a metal substrate comprising the steps of applying a layer of a compound selected from the group consisting of molybdates and tungstates of an element selected from the group consisting of Li, Na, K, Rb, and Cs, to at least a portion of the surface of said substrate, and heating said surface layer in a reducing atmosphere to a temperature of about 600 C. to convert said layer to a black surface layer consisting of an oxidic compound of a metal selected from the group consisting of molybdenum and tungsten and one of said elements.

3. A method of forming a black surface layer on a 3 4 metal substrate comprising the steps of applying a layer References Cited of lithium trimolybdate to at least a portion of the sur- UNITED STATES PATENTS face of the substrate, and thereafter heating said surface 2 472 189 6/1949 Bienfait et a1 117*225 X layer to a temperature of about 600 C. in a reducing 3189476 6/1965 Cowan 117 227 atmosphere to convert the same into a black surface layer. 5 3:215:555 11/1965 Krey X 4;. A method of forming a black surface layer on a nickel substrate comprising the steps of applying a layer FOREIGN PATENTS of lithium trimolybdate to at least a portion of the sur- 241,304 10/1925 Great Britain. face of the substrate, and thereafter heating said surface layer to a temperature of about 600 C. in hydro- 1O ALFRED L'LEAVITT Pnma'y Exammer gen to convert the same into a black surface layer. 1. R. BATTEN,JR., Assistant Examiner. 

2. A METHOD OF FORMING A BLACK SURFACE LAYER ON A METAL SUBSTRATE COMPRISING THE STEPS OF APPLYING A LAYER OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF MOLYBDATES AND TUNGSTATES OF AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF LI, NA, K, RB, AND CS, TO AT LEAST A PORTION OF THE SURFACE OF SAID SUBSTRATE, AND HEATING SAID SURFACE LAYER IN A REDUCING ATMOSPHERE TO A TEMPERATURE OF ABOUT 600*C. TO CONVERT SAID LAYER TO A BLACK SURFACE LAYER CONSISTING OF AN OXIDE COMPOUND OF A METAL SELECTED FROM THE GROUP CONSISTING OF MOLYBDENUM AND TUNGSTEN AND ONE OF SAID ELEMENTS. 